The component elements of standard head suspension assemblies (HSAs) include a base plate, a resilient region, a load beam, a flexure and a head slider. The base plate is positioned at a proximal end of the load beam, adjacent to the resilient region, and is configured for mounting the load beam to an actuator arm of a disk drive. The flexure is positioned at a distal end of the load beam. Mounted to the flexure is a head slider with a read/write head mounted thereon, which is thereby supported in read/write orientation with respect to an associated disk. The base plate, the resilient region, the load beam and the flexure can each be configured as separate elements attached to each other, or two or more adjacent elements may together be configured as a single, one-piece element to which other elements or components of the HSA are attached.
A conventional flexure, sometimes referred to as a Watrous gimballing flexure, is a single element configured with a pair of outer flexible arms about a central aperture with a cross piece extending across and connecting the arms at a distal end of the flexure. A flexure tongue is joined to the cross piece and extends proximally from the cross piece into the aperture. A free end of the tongue is centrally located between the flexible arms. The head slider is mounted to the free end of the flexure tongue.
The head slider is mounted to the flexure tongue so that the plane of the air bearing surface of the head slider is in a predetermined (e.g., planar and parallel) relationship to the plane of the disk surface. During manufacturing and assembling of the HSA, any lack of precision in forming or assembling the individual elements contributes to a lack of planarity in the surfaces of the elements. A buildup of such deviations from tolerance limits of planarity and other parameters in the individual elements can cause deviation from desired planar parallelism to the associated disk surface in the final HSA. The parameters of static roll and static pitch torque in the final HSA result from these inherent manufacturing and assembly tolerance buildups.
Ideally, for optimum operation of the disk drive as a whole, during assembly of the head slider to the flexure tongue, the plane of the load beam mounting surface datum (to which the load beam is mounted during HSA assembly) and the plane of the head slider air bearing surface datum must be in a predetermined relationship to each other. The load beam mounting surface datum and the head slider air bearing surface datum are planar surfaces used as reference points or surfaces in establishing the planar parallelism of the plane of the actuator mounting surface and the plane of the air bearing surface of the head slider surface relative to each other. The upper and lower planar surfaces of the head slider are also manufactured according to specifications requiring them to be essentially or nominally parallel to each other.
Static roll torque and static pitch torque have their rotational axes about the center of the head slider in perpendicular directions, and are caused by unequal forces acting to maintain the desired planar parallelism on the head slider while it is flying over the disk. That is, static torque is defined as a torque or a moment of force tending to cause rotation to a desired static (i.e., reference) attitude about a specific axis (in this case, the roll axis or the pitch axis of the HSA).
As applied to an HSA, the axis of static roll torque is coincident with the longitudinal axis of the HSA. The value of static roll torque is measured on either side of the static roll torque axis when the plane of the flexure tongue is in a predetermined relationship (ideally parallel) with the plane of the base plate. If the flexure has been twisted about the static roll torque axis during manufacture (i.e., there is planar non-parallelism of the flexure tongue with respect to the disk along this axis), the values measured on either side of the roll torque axis will not be the same. Thus, when the attached head slider is in flying attitude to the associated disk surface, a force (referred to as an induced roll torque value) is needed to twist the tongue back into planar parallel alignment to the disk.
The axis of pitch torque is perpendicular to the longitudinal axis of the HSA, and thus to the axis of roll torque. The value of static pitch torque is measured on either side of the static pitch torque axis when the plane of the flexure tongue is in a predetermined relationship (ideally parallel) with the plane of the base plate. If the flexure has been twisted about the static pitch torque axis during manufacture (i.e., there is planar non-parallelism of the flexure tongue with respect to the disk along this axis), the values measured on either side of the pitch torque axis will not be the same. Thus, when the attached head slider is in flying attitude to the associated disk surface, a certain force (referred to as an induced pitch torque value) is needed to twist the tongue back into planar parallel alignment to the disk. It will of course be understood that under actual conditions the flexure may need to be twisted with respect to both axes, to achieve alignment about both the pitch axis and the roll axis.
These torques can also be referred to in terms of static attitude at the flexure/slider interface and in terms of the pitch and roll stiffness of the flexure. The ideal or desired pitch and roll torques are best defined as those which would exist if the components were installed in a predetermined relationship (ideally, planar parallel) configuration in a disk drive. In an actual disk drive, pitch and roll static torques produce adverse forces between the air bearing surface of the slider and the disk, affecting the flying height of the slider above the disk, resulting in deviations from optimum read/write and head/disk interface separation.
In a conventional flexure design, the flexure tongue is offset from the flexure toward the head slider to allow gimballing clearance between the upper surface of the head slider and the lower surface of the flexure. This offset is formed where the flexure tongue and cross piece join, in conjunction with forming the dimple on the flexure tongue. This standard flexure design evidences a low value of pitch stiffness and a moderate value of roll stiffness. Pitch stiffness and roll stiffness are each measured in force X distance/degree. Thus, in developing a new design for a flexure, it would be most desirable to provide a flexure and a method of fabrication which would accurately compensate and correct for manufacturing variations that currently contribute to static pitch and roll torque errors. The manufacturing process should be efficient to perform corrections for both static roll torque and for static pitch torque, since the ability to correct for both static torques is needed for proper flexure/slider alignment.
For years, the disk drive industry has been striving to reduce static attitude error and to thereby make head sliders fly more consistently. Several potential solutions to the problem of static attitude error have been proposed. One potential solution involves bringing the head slider and the flexure bond pad into close proximity to each other in the desired attitudinal relationship, and then fixing them together in the aligned position with adhesive. The adhesive would become a structural element of the HSA used to fill voids and to do "difficult" bonds.
Harrison, at al., in The Double Dimple Magnetic Recording Head Suspension and Its Effect on Fly Height Variability, Transactions of the American Society of Mechanical Engineers; Journal of Tribology, 94-Trib-39, 1994, describes a Double Dimple suspension assembly. According to Harrison, et al., the head slider mounting surface on the underside of the flexure has a dimple which is convex to the confronting surface of the head slider. The dimple on the flexure has a concave surface which is positioned to confront the convex surface of the load bearing dimple on the load beam. The radius of curvature of the dimple on the flexure is larger than the radius of curvature of the load bearing dimple on the load beam, so that there is a single point of contact between the convex surface of the load bearing dimple on the load beam and the concave surface of the dimple on the flexure. The head slider is allowed to pivot about the convex surface of the dimple on the flexure during assembly to achieve mutual planar parallelism between the plane of the head slider air bearing surface and the plane of the load beam mounting surface. Then, gaps between the head slider and gimbal flexure around the flexure dimple are filled with bonding adhesive. Thus, during assembly, the mounting surface of the head slider is said to register to the convex surface of the dimple without twisting the flexure. The pivoting necessary for the head slider to follow undulations of the disk after assembly and during operation is said to occur at the point of contact between the concave surface of the dimple on the flexure and the convex surface of the load dimple on the load beam.
Although the Harrison Double Dimple concept offers certain advantages, having the load point and bond out feature nested contributes added complexity to the construction and assembly of the HSA. Also, if the individual elements are misaligned, an additional torque can be contributed due to the nested misalignment. It may be possible that this new torque is exactly correct to obtain proper flyheight, but, in order to do so, the bonding must be done at the precisely correct Z-height.